What kind of political systems should there be? In this paper I examine two competing principles of institutional design — an instrumental view, which maintains that one should design institutions so as to realize the most plausible conception of justice, and a democratic view, which maintains that one should design institutions so as to enable persons to participate in the decisions that impact their lives. I argue for a mixed view that combines these two principles. In the second stage of the argument, I draw on this principle of institutional design to argue for the need for suprastate institutions. These are required to protect persons’ core basic rights and, over and above that, they are needed to provide fair and legitimate procedures for choosing which rules should govern the global economy and environment. The third stage of the argument develops this account by elaborating on what features global institutions must possess for them to perform these two distinct kinds of roles